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What is progesterone ?

Progesterone is a hormone (a chemical messenger) produced by the ovaries that is necessary to support pregnancy. Progesterone is produced by the corpus luteum of the ovary after ovulation; and is essential for ripening the uterine lining so that the embryo can implant in it. Progesterone rises in the blood following ovulation, peaks on Day 20, and then declines .

Luteal Phase Defect and progesterone

The luteal phase is the second half of the menstrual cycle during which the corpus luteum produces progesterone to maintain the endometrial lining of the uterus so that an embryo can implant in it . When the corpus luteum stops producing progesterone , it disintegrates , and because the uterine lining no longer gets the progesterone support It needs, it gets shed, and the period begins.

What is the Progesterone blood test Used For?

It is useful to determine if ovulation has occurred.

The Results of the Progesterone Test

The progesterone level should be more than 15 ng/ml about 7 days after ovulation. This suggests that the corpus luteum is functioning normally. A low Day 21 progesterone levels suggests the cycles was anovulatory (no egg was produced).

Low progesterone and miscarriages

Some doctors believe that low progesterone levels during the luteal phase can cause miscarriages. However, this concept of a luteal phase defect is now considered to be controversial .

Progesterone levels after embryo transfer

Luteal phase supplementation with progesterone is routinely performed after an embryo transfer during an IVF cycle, to help support the endometrium. Some doctors measure progesterone levels 4-6 days after embryo transfer; and if the levels are low, they increase the dose of progesterone given.

Check your own progesterone levels

If you live in the USA, the good news is that you can now check your progesterone levels yourself.

Need help in making sense of your lab results ? Please enter your lab values and your clinical or Fertility center details in our Free Second Opinion form and I'll help you interpret your results !

Using progesterone for treatment

Since progesterone is such a key pregnancy hormone, it's often used for treating infertility. However, lots of infertile women are confused about what progesterone does. They know that it is present in birth control pills; and that it is used to induce a period when this is overdue. Therefore, when their doctor prescribes the same progesterone when they are pregnant, explaining that it is being used to support the pregnancy, they are very confused. How could a hormone which is being used to bring on a period possibly also be used for supporting a pregnancy ? It just does not make any sense.

Actually, it does ! Progesterone is the hormone which the corpus luteum in the ovary produces to help during the implantation of the embryo . It creates secretory changes in the uterus lining, so that it is ready to receive the embryo. This is why it's role in supporting the pregnancy is quite straightforward. Even the name, pro (= for, towards, helping) -gest (= pregnancy) -erone (= steroid hormone) suggests this role - it supports the pregnancy !

So how is this used to induce a period ? Remember that it's not the progesterone per se which induces the period. In fact, if you take progesterone for long periods of time in high enough doses, the period will get indefinitely postponed. When your doctor induces a period for you with progesterone, he gives it only for a short amount of time - for about 3-5 days . The period starts 3-8 days after you stop the last tablet of progesterone , because the uterine lining has lost the support the progesterone was providing. This is why this progesterone induced bleeding is called a withdrawal bleed - it's the withdrawal of the progesterone which causes the onset of the period (just like it does in a normal menstrual cycle , when the corpus luteum dies and stops producing progeserone because there is no embryo to produce HCG to rescue it !)